PURPOSE: A prepolymer for fiber-reinforced composite material, excellent in flow and capable of providing a polyamide of excellent heat resistance, obtained by using oxyNadic acid as a chain terminator and reacting a specified carboxylic acid component with a diamine component.

CONSTITUTION: A prepolymer is produced by using oxynadic anhydride of formula I as a chain terminator and reacting a carboxylic acid component comprising 3,3',4,4'-benzophenonetetracarboxylic anhydride of formula II and 5-(2,5- dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride of formula III with a diamine component comprising a polyamide of formula IV. In this way, the purpose prepolymer in which both of the terminals are represented chiefly by formulas V and/or VI and which is used for fiber-reinforced composite materials can be obtained. This prepolymer shows fluidity at a temperature as low as 160°C or below.